A conventional objective lens driving means provided in the optical pickup of an optical disc drive is composed of a moving part on which an objective lens is mounted, support members for supporting the moving part, focusing coils, tracking coils, a yoke, and magnets.
When a drive current is applied to the focusing coils, electromagnetic force is produced by the interaction of the current with the magnetic flux developed by the magnets. The electromagnetic force drives the moving part in the focusing direction, which is either toward or away from the optical disc surface. Similarly, when a drive current is applied to the tracking coils, electromagnetic force is produced by the interaction of the current with the magnetic flux from the magnets. The electromagnetic force drives the moving part in the tracking direction, which is the direction radially with respect to the optical disc.
If the optical disc is bent or obliquely mounted with respect to the optical axis of the objective lens, when the light collected by the objective lens passes through the substrate of the optical disc, coma aberration is caused, and the focusing spot spreads, resulting in a problem that information cannot be accurately recorded or read. Thus, a mechanism that adjusts inclination of the objective lens in accord with such bend or inclination of the optical disc is required.
When the vertical positional relationship between the optical disc and the objective lens is considered such that the optical disc is the top and the objective lens is the bottom, in cases in which the optical disc is bent upward, the optical disc is farther away from the objective lens, and in cases in which the optical disc is bent downward, the optical disc is closer to the objective lens. In such case, in order to focus the objective lens on the optical disc, the objective lens is moved upward in the case of the optical disc bent upward, and the objective lens is moved downward in the case of the optical disc bent downward.
In this case, if structured in such a way that the objective lens is inclined toward the inner periphery of the optical disc when moved upward in the focusing direction, and the objective lens is inclined toward the outer periphery of the optical lens when moved downward in the focusing direction, since the direction of a bend of the optical disc and the direction of inclination of the objective lens can be adjusted, influence of such bend of the optical disc can be reduced.
Patent Document 1 discloses an example of a conventional structure of such objective lens driving means of the optical pickup. In Patent Document 1, a magnetic body is disposed so that the center point of movement of the coil and the center point of the magnetic body are separated from each other in a direction perpendicular to the optical axis of the objective lens. Further, the coefficient of elasticity of the elastic members that movably connect lens supporting members that support the objective lens and a fixing member is different between the left side and the right side of the optical axis of the objective lens.
[Patent Document] JP Patent Publication (Kokai) No. 2001-93178 A (pages 3-4, FIG. 1)